Burning head of penis but all STD testing came back neg, had blood at top where foreskin attacth to head and stinging mostly if sweating, went to doc and determined it'd not a STD so what could it be if it's not a std?

Inflammation... Can cause stinging and bleeding. This could be from mechanical irritation of that region on clothing. Certain bacterial and fungal infections can cause burning and itching, and do not show up on standard std or UTI tests. There are inflammatory conditions of the skin, or types of dermatitis, such as lichen sclerosis that are problematic. I recommend seeing a dermatologist or urologist.